Chemical composition and metal-treatment process



:52. comPosmous. l. 4: *7

Patented Jan. 20, 1931 Cross Reference PATENT OFFICE IRAN! D. BURKE, OF ROCKY RIVER VILLAGE, OHIO, ASSIGNOB TO THE PABSIVATIOH PBDDUGIS COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF DELAWARE CHEMICAL COEPOSITION AND METAL-TBEATHENT PBOCEBS Io Drawing.

This invention relates to the treatment of metal such as iron and iron compounds or alloys and in particular to the process and bath used inconnection with such treatment,

which ma be for the purpose of cleaning, rust-proo glor rendering the metal highly resistant to t e attack of acid or corrosion.

In the art of pickling, which is one of the important phases of this invention, the metal 10 is treated with dilute acids to remove rust and scale, after which the metal is dipped into an alkaline bath and washed with water "to remove the last traces of free acid. The acid removes the rust and scale but unfortunately from the pickling standpoint it attacks the cleaned metal itself, producing an evolution of hydrogen gas which escapes into the air, carrying with it a fine spray of the 5 pickling bath producing an atmosphere of great rusting properties and one which is highly injurious to the health of the workers exposed thereto.

The attack of the pickle on the metal itself not only wastes valuable metal but also uses up the strength of the acid which should be directed to removing the rust and scale. Another disadvantage resulting from the action of the acid on the metal in the above process is that it causes the metal to become brittle, or the effect which is commonly referred to as hydrogen embrittlement. I The action of acid in the pickling bath is to dissolve the scale, but unless the article treated is removed from the pickling bath at the instant when the scale is completely dissolved, further solvent action takes place on the metal itself, causing pitting and roughening of the surface. This secondary action great- 4 ly depreciates the value of the finished product.

Another objection to the straight acid solution pickling bath is found in the close attention that must be paid to the concentration of acid in the bath and to the temperature of the bath. If these two conditions are i not kept within certain limits excessive attack of the metal may result or the opposite Application fled February 18, 1928. Serial No. 840,648.

dling and storage of the metal articles that have been treated by the process above referred to for in their cleaned condition they are more susceptible to rusting and corrosion than they were before cleaning.

The transporting of sulphuric acid in iron and steel tank cars is not entirely sat sfactory for the reason that sulphuric acid in dilute and moderate concentrations attacks iron and steel very readily. The concentration of sulphuric acid, therefore, that may be economically. trans orted in iron and steel tank cars is restricte to the higher strengths of acid.

In order to overcome these and other objections various compounds and materials have been proposed to be added to a pickling bath I Examiner and to acid that is transported or stored in metal containers and for the rust-proofing of metals b an acid process to'vary and modify the e ect of the acid upon the metal. Such substances are commonly referred to as regulators or inhibitors several of which are known and in use at the present time.

These regulators and inhibitors vary in efiiciency, depending apparently upon their nitrogen, sulphur or phosphorus content, their molecular weight, their basic character and general chemical composition. Their use is often restricted to hydrogen inhibition alone and hence they do not impart an rust resistance to the cleaned article e film formed by many of the known inhibitors is restricted to the cathode areas of the article to be cleaned and hence articles cleaned by such solutions show characteristic pitting and etchin at the anode areas.

Again many 0 hibitors do not combinechemically with the cleaned metal and hence the film deposited by them upon the metal is apt to be both spotted and non-adherent.

Some inhibitors such as aldehydes and quinoline impart undesirable odors to the cleaning bath and the surrounding atmosphere. Many of the known inhibitors such the commonly used in-' as: thiourea, quinoline 'ethioidide, etc. are I costly and their use and availability for large commercial and manufacturing processes is limited and practically prohibited thereby.

One of the objects of this invention is to lOO 252. comPosmous.

ll 4 7 t provide a liquid to remove from the surfaces of metallic articles scale, rust, grease and other foreign materials without appreciably attacking the pure metal, of the surface. Another object of this invention is to rustproof the surface of the cleaned metallic article and to render it practically inert to the action of the corrosive substances that it is apt to come in contact with.

Another object of this invention is to prevent the escape of rust forming and promoting elements as well as poisonous and objectionable vapors from the pickle -vat.

Another object of this invention is to prevent over-pickling and etching and pitting of the work as well as to economize in the acid consum tion of the pickling process.

Another object of this invention is to minimize the amount of metal lost in the pickling process, and to provide a pickling bath that will concentrate its energies to the removal.

' of rust, scale and foreign materials from the metal surfaces. 0

Another object of this invention is to provide a pickling bath that will remove rust and foreign matter from polished, machined and finished stock without appreciably altering the dimensions or affecting the finish thereof.

Another object of this invention is to increase the efiiciency of the pickling operation by permitting a wider range in the acid con; tent and in the temperature of the bath and by generally speeding up the process. Another object of this invention is the prevention of brittleness or hydrogen embrittlement of metals subjected to the pickling process which is one of the contributory causes of corrosion fatigue.

Another object of this invention is to provide a means for preventing the corrosion of iron and steel tanks and containers used in connection with the. transportation and storage of sulphuric acid in dilute and moderate concentrations.

Another object of this invention is to provide a process for the treatment of metallic surfaces whereby the treated article is cleaned and completely covered with a protective coating that is effective in preventing the oxidation and corrosion of the metal for long periods of time.

Another object of this invention is to prometal surface to form a highly adherent sur-- 'face covering. v

A further object of this invention is to provide an eflicient and inexpensive regulator or inhibitor that may be readily obtained from a variety of cheap and abundant materials.

These and other objects and advantages of my improved roduct and method of metal treatment wifi be made apparent from Examiner the ensuing description and specification and the novelty and scope of the invention will be particularly pointed out in the appended claims.

- Stated in general terms my invention con? sists in selectively controlling and inhibiting' the action ofan acid solution upon met als and in effecting the deposition of a prometal exposed thereto with the evolution of hydrogen and the metal is thereby cleaned. It is obvious that although the acid will dissolve the scale and rust it will also attack the pure metal and hence this method is an example of a complete surface etching with no distinctiop made between pure metal and metallic oxides such as rust and scale.

- If however, to the acid solution, which may be, for example, hydrochloric, sulphuric or phosphoric acids or mixtures thereof-dissolved in water, there be added an inhibitor, the acid attack will be more or less localized upon the existing rust and scale and the clean metallic surface will be comparatively unafi'ected. A theoretically perfectinhibitor is therefore one which will completely restrict the acid attack to the surface impurities such as rust and. scale and which will have no ac tion upon the pure clean metal.

There are many inhibitors both organic and inorganic known to industry although their use is more or less restricted by their limitations.

Extensive personal research has indicated that many organic materials or compounds containing either nitrogen, sulphur or phosphorous and the halogens either individually or associated together are good inhibitors. The nitrogen is usually present in the amino form giving the substance either basic or amphoteric properties; the sulphur usually replaces oxygen and the halogens are usually present as derived or substituted compounds.

Research also indicates that inhibitory power generally increases with increased molecular weight, provided the substance has the necessary contained element or groups of elements in the proper grouping or binding. It also indicates in general that inhibition is at a maximum when the inhibitor is amphoteric, thatis, when the inhibitor will possess either acid or basic properties depending upon the external conditions. It further indicates that inhibition is at a maximum within the colloidal realm.

With these facts in mind a search was of the albuminoid keratin.

made for the best possible inhibitor with the result that the amino acids and particularly those derived from animal proteins possessed in the largest degree the qualities sought.

A large percentage of the external covering and structure of animals such as hair, horns, hoofs, skins, bones, etc., contains a high percentage of'very complex organic compounds called proteins consisting mainly These proteins are colloids and have extremely high molecular weights. They contain carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus in complex association or grouping. Upon hydrolysis (treatment with either steam, acids or alkalies) these complex proteins are broken down into a series of socalled amino-acids with the type formula:

. in which the radical or radicals (R) contain solution.

the sulphur, some nitrogen and the phosphorus. The indicated amino and carboxyl groups also show the required amphoteric qualities of derived protein acids.

These protein acids can therefore be prepared b extracting'and dissolving animal hair, hi es, horns, hoofs, bones, etc., in either a hydrochloric, sulphuric or phosphoric acid The product of such hydrolysis will be a mixture of these so-called aminoacids including the amino-acid cystine. The product may be purified by either precipitation or coagulation using such typical precipitating agents as sodium acetate, ammonium sulphate or sodium chloride. The

precipitate may then be decolorized and a regulator or inhibitor to a suitable acid pickling'solution, made up from acids such as hydrochloric, sulphuric or phosphoric or mixtures thereof for the following reasons: (1) Its presence in the acid solution will restrict the acid attack to the rust and scale and very materially decrease the rate of metal solution in the acid. (2) Its presence in the acid solution will cause to be deposited upon the cleaned metal an absorbed colloidal film which, upon drying the cleaned metal, aids to protect it against further rusting or corrosion. This colloidal film is a compound formed in the acid solution between the metal resistant properties.

In preparing the compound dissolve the animal proteins, which may be animal hides,

horns, hoofs, bones or mixtures thereof, in strong sulphuric, hydrochloric or phosphoric acid or mixtures thereof using gentle heat if necessary. When solution is complete, coagulate the hydrolyzed product by .the addition of some reagent of the Hofmeister series, such as sodium acetate, ammonium sulphate or sodium chloride.

Filter or decant the liquid and the solid coagulate will be the unpurified proteIn amino-acid mixture.

To purify the product completely wash the coagulate free from dissolved impurities with warm water and decolorize by mixing with a suitable decolorizing material such as animal charcoal, fullers earth or some similar absorbent. Or, if a high degree of decolorization is required, redissolve the coagulate in strong sulphuric acid and add to this acid solut'on a definite amount of bone black or a similar substance. Then filter and recoagulate with sodium acetate. This pu11i-' fied product may then be carefully dried if desirable or necessary, and in either the wet or d1 form is ready for use as a regulator or in ibitor.

One of the important uses of the-above product or regulator is in the art of metal cleaning. Metal cleaning is concerned primarily with the removal of mill scale and rust from metals or metallic alloys. This scale and rust is not uniform in thickness or adherence as a rule and when portions have been removed clean metal surfaces are exposed to acid attack by the cleaning solution. There are therefore, taking the cleaning of iron as a typical example, two main reactions taking place in'a cleaning acid bath:

rust and scale sulphuric acld=water iron sulphate This is the desired action.

iron sulphuric acid=iron sulphate hydrogen is the dissolving of the clean metallic surface.

This latter reaction (2) is an undesirable reaction. The addition of my improved regulator to the pickling bath will materially decrease the evolution of hydrogen and consequently repress reaction (2) (acid attack on the pure metal surface) while having very little effect upon reaction (1) 52. couPosmous.

In a straight acid bath these cathode areas occur principally at the grain boundaries in steel or between the metal and the slag in wrought iron. Hence there is a constant loss of dissolved iron from the anode areas in the metal and a consequent discharge of hydrogen at the cathode areas. This anode area loss is easily recognized by pitting and etch- 1n Now, if to the acid bath, there is added a slfiallamount of my regulator, it will behave iii solution as a positively charged colloid and therefore it first travels to the cathode areas with the hydrogen and is-there discharged and absorbed by the cathode areas.

While this preliminary action is going on the acid is dissolving the iron oxide from the metal by reaction. (1) As the dissolved iron is anodic in the solution, in a short time a more or less definite equilibrium is reached with a consequent shifting of polarity, the cleaned metal becoming practically completely cathodic. The dissolved-iron or iron oxide also reacts'with the regulator to form an iron salt of the amino-acids and, this being 7 a positively charged body, also travels to the the scale and rust.

cleaned metal and is there discharged and absorbed on the whole metallic surface completely covering the same.

As a result of these reactions there is built up upon the cleaned metal a protective colloidal film because the positively charged colloidal particles are comparatively heavy and cannot escape by gaseous evolution.

The presence of this film serves two distinctive purposes: First, by its presence on" the cleaned metal -it polarizes the hydrogen,

ion, preventing its electrical discharge and hence its conversion to the gaseous state thereby practically completely restricting the acid attack to reaction (1) the dissolving of Second, when this film has ben dried out, it being an iroii compound of the amino-acids and absorbed upon the cleaned metal it has very definite rustor oxidation resistant properties effectively rustproofing the metal. I

Therefore, by the use of these amino-acids derived from animal proteins, it is possible tion and storage of less than concentrated soto clean metallic surfaces of rust and scale and effectively rust proof them at the same time. K

From the analysis of the behavior of my improved regulator or inhibitor it is apparent that another important use to which it could be put is in connection with the transportalutions of sulphuric acid in iron and steel containers. The addition of a small amount of amino-acids of the type disclosed to the sulphuric acid would prevent its attack upon the metallic container in the manner previously described greatl decreasin the handling costs of dilute s huric aci In the practical use 0 my improved regu- Cross- Reference- Iator or inhibitor a satisfactory pickling bath ma be prepared as follows:

o a 5% solution of sulphuric acid add 2% by weight of regulator, Immercethe articles to be cleaned and rust proofed in this solution, which may be heated to 160 R, if desired, and may also be agitated. Allow the articles to remain in the solution until clean and until they show the-characteristic film formation produced on the metal surfaces by my regulator.

The time of immersion varies with the amount of scale and rust present on the material and with the degree of rustproofin required. When clean and the film forme the article is removed from the bath and washed free from excess acid byimmersion in a hot weakly alkaline solution (2% sodium carbonate solution). The materials are left long enough in this alkaline wash so that by reason of their absorbed heat, they will completely and quickly dry off on removal. They are then clean and rust proofed.

The acid concentration of the bath may be between the limits of a fraction of one rel cent and twelve per cent depending upon the speed of cleaning desired and the temperature at which the process is carried on.

The regulator may be used in any concentration up to 10%, depending largely upon the acid concentration and the temperature of the bath which may be varied considerably from the figure stated.

In place of sulphuric, hydnochloric or phosphoric acids or their mixtures, other acids or mixtures thereof may be used in the pickling bath depending upon various factors, such as speed, cost, temperature, type of metal etc., to be determined in each case.

The treatment of iron and its alloys was cited as merely illustrative of some of the uses ,of my improved inhibitor. Its use is not liniited to iron and similar efl'ects are produced when other metals are substituted for iron in the above procedure.

. It has been found that my improved regulator may be used to advantage in connection with boilers and hot water heating systems to prevent scale formation. By the addition of slnall amounts of acid and my regulator from time to time to the feed water of the boiler a protective coating is formed upon the boiler surfaces which practically completely prevent scale formation and at the same time doesnot impair the efliciency of the boiler.

It is to be understood that the examples cited in general, represent the optimum conditions and that there is considerable latitude allowed as to quantities and roportions that can be used before losing al the beneficial effects of my invention.

Furthermore, the foregoing procedure, uses and compou s are cited for urposes 'faxamiaer i of illustration and explanation so t at those ical action of the acid on the skilled in the art will be able to practice the invention, which is not limited to details of procedure, or to the precise ingredients mentioned, or to mere matters of form, or otherwise than as the prior art and the appended claims may require under and subject to the range of equivalents appropriate in chemical cases.

I claim:

1. The method of cleaning or 'treating metals which comprises subjecting the same to a cleaning acid bath and inhibiting the chemical action of the acid on the pure metal by incorporating in the acid bath a small amount of alpha amino-acid.

2. The method of cleaning or treating metals which comprises subjecting the same to a cleaning acid bath and inhibiting the chemical action of the acid on the pure metal by incorporating in the acid bath a small amount of aromatic amino-acid.

3. The method of cleaning or'treating metals which comprises subjecting the same to a cleaning acid bath and inhibiting the chemical action of the acid on the pure metal by incorporating in the acid bath a small amount of amino-acids comprising hydrolyzed proteins of animal origin. I

4. The method of cleaning or treating metals which comprises subjectin the same to a cleanin acid bath and inhibiting the chemical action ofthe acid on the pure metal lay-incorporating in the acid bath a small amount of hydrolyzed animal proteins.

5. The method of cleaning or treating metals which comprises subjecting the same to a cleanin acid bath and inhibiting the chemical action of the acid on the pure metal by incorporating in the acid bath a small amount of a sulphur-containing amino-acid.

6. .The method of cleaning or treating metals which comprises subjecting the same to' a cleaning acid bath and Inhibiting the chemure metal by incorporating in the acid ath a small amount of hydrolyzed animal proteins including the albuminoid keratin.

7. The method of cleaning or treating metals which comprises subjecting the same to a cleaning acid bath and inhibiting the chemical action of the acid on the pure metal by incorporating in the acid bath a small amount of the amino-acid cystine.

8. A non-oxidizing mineral acid bath for cleaning and treating metals containing a small amount of alpha amino-acid.

9. A non-oxidizing mineral acid bath for cleaning and treating metals containing a small amount of aromatic amino-acid.

10. A non-oxidizing mineral acid bath for cleaning and treating metals containin a small amount of amino-acids comprising iydroylzed proteins of animal origin.

11. A non-oxidizing mineral acid bath for cleaning and treating metals containing a too 

